The invention relates to an arrangement for adjusting the rotor blades of a propfan turboprop engine having two counter-rotating propfan rotors which are driven by two turbines by means of separate concentric shafts disposed in a housing. Adjusting rings which can be rotated in circumferential direction and are kinematically coupled with two rotor blade rings are arranged axially behind one another.
An arrangement of this type is known, for example, from German Published Unexamined Patent Application (DE-OS) 36 14 157. In this arrangement, two propfan rotors are arranged radially outside the turbines of the gas turbine engine to be driven. In this case, the constructive design of an adjusting arrangement for the propfan blades is not critical since stationary housing parts are available in the surroundings of the adjusting arrangement which are required for supporting the adjusting forces. The particular disadvantage of this construction is that the hot combustion gases are guided around the adjusting arrangement and result in thermally caused imprecisions. In addition, the thermal stress to the adjusting arrangement is extremely high. Gearless variants of propfan turboprop engines of this type can be mounted without any problems only at the tail of the airplane and, for transmitting forces from the driving low-pressure turbine to the fan blades, require an expensive and heavy frame construction.
In the case of a propfan engine where the propfan blades are located in front, for example, according to German Published Unexamined Patent Application (DE-OS) 36 11 792, these aerodynamic disadvantages do not occur. The previously known engines have a working turbine which is coupled with the two counter-rotating propfan blade rings by way of a step-down gear. The step-down gear, which is arranged in the area radially inside the propfan blade rings, is supported at stationary housing parts. Thus, also in this case, the accommodation and support of adjusting arrangements for the swivelling of propfan blades is not critical. However, this type of a gear has an extremely high weight because high outputs must be processed. In turn, this high weight is a disadvantage because it increases the take-off weight of the airplane which has an unfavorable effect on the economical aspects of the airplane. In addition, a gear reduces the reliability of the engine.
It is an object of the present invention to provide an adjusting arrangement of the type mentioned above which permits a precise adjustment of the rotor blades of both propfan rotors and thus an adaptation to varying conditions of flight.
According to the invention, this object is achieved by providing an arrangement wherein the adjusting rings are coupled by means of a planet wheel gear which has a number of double-toothed planet wheels which are fastened to a rotatably disposed web, the web being supported on the side of the housing by means of planet members disposed on one of the propfan rotors, and wherein the toothings which are in operative connection with the adjusting rings, are dimensioned such that when the rotational speed ratio of the propfan rotors is fixed, no relative movements occur of the adjusting rings.
The arrangement according to the invention has the advantage that it is possible to introduce the reaction forces required for the adjusting into the engine housing, although the propfan rotor, which is away from the housing, has no possibility for a direct support in the housing.
In a preferred construction of the invention, the rotational speeds of the two shafts are in a geometrically fixed relationship to one another. In particularly preferred embodiments, the rotors are to rotate at an oppositely identical rotational speed. This is achieved by providing in the engine, for example, in the area of the turbines, one or several toothed wheels which mate with both shafts and thus define the fixed rotational speed.
According to preferred constructions of the invention, an adjusting motor is supported in the first rotor and is in operative connection with both adjusting rings; i.e., one rotating movement relative to the first rotor is introduced directly into the first adjusting ring and by way of corresponding intermediate members, into the second adjusting ring.
According to an alternative construction of the invention in which the shafts are not synchronized with respect to one another and thus the rotational speeds are not fixedly coupled with one another, these can freely adjust themselves depending on the load absorbed at the rotor blades. In this case, the balancing of moments in the propfan rotors is produced by the free blade adjustment.
If the operating condition of the existing equilibrium of moments changes such that one of the propfan rotors absorbs less work, the turbine stage coupled with it endeavors to increase its rotational speed. The rising of the respective shaft speed now causes the blade adjusting mechanism according to the invention to adjust the blade such that the fan stage again absorbs more work whereby the shaft speed is lowered again. If the rotor blades are loaded more, the turbine speed will decrease, and the rotor blades are moved into a position of less load, whereby the turbine speed increases again. This control applies to both propfan rotors because they are coupled with one another by means of the wheel system according to the invention. In this case, the wheel system is preferably designed such that, when the rotational speed of the propfan rotors is commensurate but opposed, no relative movements take place in the adjusting system.
A preferred further development of the invention provides that an adjusting motor is provided which is supported in the housing, by means of which an additional adjustment of the rotor blade rings is possible. As a result, in addition to the automatically functioning balancing control, a blade adjustment may be superimposed by means of which, for example, the engine may be adjusted to reversed thrust. The arrangement has the significant advantage that the adjusting motor required for the blade adjustment does not rotate along but is stationarily supported in the housing. As a result, the energy supply to the motor may take place in a simple manner. In addition, this arrangement permits a fast exchange of a defective motor.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.